pneumatic valve springs
Posted by:
Peter Heid (IP Logged)
Date: February 08, 2002 10:34PM
<HTML>I am a Formula 1 fan, mostly because exciting technological innovations usually happen here first and then outlawed here first. An engineer for Mcclaren said most of his 15 years were spent developing ideas that were later banned. The most intriguing development currently in use is the pneumatic valves (actually just the springs) enabling engine RPM's to exceed 19,000 rpms with no valve float limit in sight. The development started by building springs, one inside the other, with tolerances just right to have drag between the springs to provide needed friction and dampen the valve, but this scheme seemed to have an upper limit of 15,000 RPM. the next step was to replace the coil spring with an air spring, the needed drag was then developed by the drag of the valve cap / plunger on the cylinder that comprises the spring pocket. From what I can gather the pressure is equalized by a pressure reservoir connecting all 40 valve pockets together and the reservoir is charged with compressed air or nitrogen from an onboard tank. You can watch the F1 pit crew recharge the tanks on some cars during a stop, watch for an air hose. The pressure, from the limited information available, seems to be run around 100 psi but each manufacturer probably uses slightly different sized plungers and cylinders. Space is limited and virtually every engine is a V-10 and has 4 valves per cylinder so I would imagine the component sizes are similar from one engine manufacturer to another. The pressure is adjusted on a dyno to give the desired engine response for each track they run.
If the engine spins 19,000 RPM then the cam at 1/2 speed is 9,500 RPM or 158 RPS. A single rotation of the cam would therefor take 0.0063 seconds and if the valve lift duration is 300 degrees of cam rotation the valve action must require 0.0053 seconds. Not bad for a rotating cam against reciprocating parts. Some F1 engineers claim the current valve system is capable of engine speeds in excess of 30,000 RPM and I believe this might be a good design direction to follow for the short cutoffs my engine design would require (theroy).
I have thought of a solenoid opened valve that is of the piston type and it uses the escaping steam from the valve stem leakage to fill an spring chamber. The chamber pressure could be regulated to provide the proper air spring function and the duration of the electrical pulse to the solenoid could be varied to change the cutoff. It would seem hard to acheive long cutoffs, actual time open, because the vapor spring would try to close the valve, working against the air solenoid (need a strong solenoid). The reaction time of the solenoid would have to be very quick, acting through a short stroke. In this case, my calculations (almost a guess) would seem to favor a maximum engine speed around 3000 RPM or greater.
The same technology is easily applied to non-electric valves as in the F1 cars. The cam opens the valves and the gas springs push them back, very simple. Steam could easily supply the pressure needed to operate the gas springs just as in the free piston engine.
Has anyone experimented with such springs for steam valves yet. If anyone is Interested I can supply more information or provide references for research.
Just Another Crazy Idea
Peter Heid</HTML>